thanks for the reply!
My problem is how to get the bounds of the polygon..
I know about intersects method and i used it in my code but sometimes it doesn't "see" that there is a collision between the rectangle and the polygon.So I assumed there's something wrong with the polygon's getbounds method..

Using the bounds of a polygon to test for intersection is using the Rectangle intersects method. Bounds => Rectangle. Using the Polygon intersects method is a different thing. To demonstrate the difference: